In recent years, as image-recording materials, materials for forming color images have been predominant and specifically, recording materials for an ink jet system, recording materials for a thermal transfer system, recording materials for an electro-photographic system, transfer type silver halide light-sensitive materials, printing inks, and recording pens have found widespread use. Also, in photographing devices such as CCDs for photographing equipment, and in LCDs and PDPs for display, color filters are used for recording or reproducing a color image. In these color image recording materials and color filters, colorants (dyes or pigments) of three primary colors of a so-called additive color mixing process or subtractive color mixing process have been used in order to display or record full-color images. In actuality, however, there is no fast colorant having the absorption characteristics capable of realizing a preferred color reproduction region and resisting various use conditions and environmental conditions. Thus, the improvement thereof has strongly been desired.
Dyes or pigments to be used for the above-mentioned uses are required to have in common the following properties. That is, they are required to have absorption characteristics favorable in view of color reproduction and have good fastness under the conditions of the environment wherein they are used, for example, fastness against light, heat, and an oxidative gas such as ozone. In addition, in the case where the colorant is a pigment, the pigment is further required to be substantially insoluble in water or in an organic solvent, to have a good fastness to chemicals, and not to lose the preferred absorption characteristics it shows in a molecularly dispersed state even when used as particles. Although the required properties described above can be controlled by adjusting the intensity of intermolecular mutual action, both of them are in a trade-off relation with each other, thus being difficult to allow them to be compatible with each other. Besides, in the case of using a pigment as the colorant, the pigment is additionally required to have a particle size and a particle shape necessary for realizing desired transparency, to have good fastness under the conditions of the environment wherein they are used, for example, fastness against light, heat, and an oxidative gas such as ozone, to have good fastness to an organic solvent and chemicals such as a sulfurous acid gas, and to be capable of being dispersed in a used medium to a level of fine particles, with the dispersed state being stable. In particular, there is a strong demand for a pigment which has a good hue and is fast to light, moist heat, and active gases in the environment, particularly for a pigment having high tinctorial strength and is fast against light.
That is, in comparison with a dye which is required to have properties as colorant molecules, the pigment is required to have more properties, i.e., it is required to satisfy all of the above-mentioned requirements as a solid of an aggregate of a colorant (dispersion of fine particles) as well as the properties as molecules of a colorant molecule. As a result, a group of compounds which can be used as pigments are extremely limited in comparison with dyes. Even when high-performance dyes are converted to pigments, few of them can satisfy requirement for the properties as a dispersion of fine particles. Thus, such pigments are difficult to develop. This can be confirmed from the fact that the number of pigments registered in Color Index is no more than 1/10 of the number of dyes.
Azo pigments are excellent in hue and tinctorial strength which are characteristics of coloring, and hence they have widely been used in printing inks, ink for an inkjet system, and electro-photographic materials. Of the pigments, yellow diarylide pigments and red naphthol azo pigments are the most typically used azo pigments. Examples of such diarylide pigments include C.I. pigment yellow 12, C.I. pigment yellow 13, and C.I. pigment yellow 17. Examples of such naphthol azo pigments include C.I. pigment red 208 and C.I. pigment red 242. However, these pigments are inferior in fastness, particularly light fastness, and hence they are decomposed when prints printed by them are exposed to light, thus being inappropriate for prints which are to be stored for a long time.
In order to remove such defects, there have been disclosed azo pigments having a fastness improved by increasing molecular weight or by introducing a group having a strong intermolecular mutual action (see, for example, patent documents 1 to 3). However, with even the improved pigments, pigments described in, for example, patent document 1 have still insufficient light fastness though improved to some extent, and pigments described in, for example, patent documents 2 and 3 have the defect that their hue is greenish and shows reduced tinctorial strength, thus being inferior in coloring characteristics.
Also, patent documents 4 to 7 disclose colorants which have absorption characteristics excellent in color reproducibility and have sufficient fastness. However, all of the specific compounds described in the patent documents have the defect that fastness is insufficient though hue is good, that hue is bad though fastness is good, or that solubility in an organic solvent or water is large, thus showing insufficient chemical fastness.
In the case of expressing a full-color image based on the subtractive color mixing process using three colors of yellow, magenta, and cyan or using four colors further including black, use of a pigment having an inferior fastness as one of the pigments would change gray balance of the prints with the lapse of time, and use of a pigment having inferior coloring characteristics would reduce color reproducibility upon printing. Thus, in order to obtain prints which can maintain high color reproducibility for a long time, there have been desired a pigment and a pigment dispersion which have both good coloring characteristics and good fastness.
Azo colorants have conventionally been utilized in various fields since they absorb various visible lights. For example, they have come into use in such various fields as coloring of synthetic resins, printing inks, colorants for sublimation type thermal transfer materials, inks for inkjet recording, and colorants for color filters. Important performance required for azo colorants as colorants includes absorption spectrum. Hue of a colorant exerts a great influence on color tone and feeling of a body colored with the colorant, giving a large effect on visual sensation. Therefore, there have long been made studies on absorption spectrum of a colorant.
Conventionally known azo dyes containing a nitrogen-containing ring as an azo component are also disclosed in patent document 5. Also, in patent documents 6 to 8, naphthol series azo pigments and colorants are disclosed wherein a benzene ring and a naphthalene ring are connected to each other through an azo group.
Further, in recent years, image display devices have been required to have a reduced size, a small thickness, a light weight, a large size, a high definition, and the like. Application thereof is widened to displays for personal computers, TV sets, gaming machines, etc., and demand for color liquid crystal displays is sharply increasing.
With such background, high color purity has become required for color filters for use in liquid crystal display elements.
As a color filter to be formed on a device for realizing a color structure in a solid-state imaging device or a liquid crystal display element, there is known a color filter comprising a yellow filter layer, a magenta filter layer, and a cyan filter layer, or a color filter comprising a red filter layer, a green filter layer, and a blue filter layer, in which such filter layers are formed in an adjacent manner in the same plane on a substrate.
In recent years, color filters have been required to have a higher definition. However, resolution has not been improved with conventional pigment dispersion systems and, since such systems have the problem that there results uneven color due to coarse particles of pigments, they have not been suited for the application which requires a fine pattern as is required in a solid-state imaging device. In order to solve this problem, there have conventionally been proposed use of dyes (see, for example, patent document 9).
It is known to use a red dye for a red filter array of a red color filter (see, for example, patent document 10).
However, a colored pattern obtained by dyes has insufficient heat resistance and insufficient light fastness, and hence there has been examined a color filter using an organic pigment having excellent heat resistance and excellent light fastness.
As a manufacturing method of a color filter using an organic pigment, there are illustrated a photolithography method in which a patterning step of exposing and developing a composition containing an organic pigment dispersed in a photo-sensitive resin, and this patterning step is repeated necessary times (see, for example, patent document 11), and a printing method such as an offset printing method using an ink containing an organic pigment and an inkjet printing method.
As organic pigments for color filters, use of organic pigments having excellent heat resistance and excellent light fastness, such as anthraquinone series, diketopyrrolopyrrole series, quinacridone series, isoindoline series, perinone series, perylene series, and condensed azo series organic pigments has been examined. These pigments, however, have the problem that they are generally difficult to disperse in a color filter and therefore difficult to provide a color filter having a high transparency.
Similarly, with a color filter comprising a yellow filter layer, a magenta filter layer, and a cyan filter layer, too, it has been desired to more improve fastness of yellow colorants for use in the yellow filter.
A proposal on a red ink composition for use in a color filter containing a monoazo compound having a naphthalene ring is made in patent document 1. However, a color filter using the compound described in patent document 1 is insufficient with respect to contrast, and it has been desired to obtain enhanced contrast.